The Issue of Machinability in Aluminium Machining
Blog | October 16th, 2018Machining, a process that’s used to form products, produces millions of metal parts every year. There are bent and drilled steel components, intricately formed alloy products, and countless other machine-formed metal items on the market. Focusing on one specific group of metals, aluminium alloys, there’s a machinability issue that requires addressing. On choosing this lightweight and ever-popular metal, problems can arise when aluminium enters a fabrication environment.
Understanding the Material Variables
Aluminium is available in many grades. There are purer forms, alloys that add copper, magnesium, zinc, and who knows how many other property-altering elements. Copper, for example, is added to increase strength. Alloying elements improve heat treatment results, change the metal’s weldability characteristics, and make aluminium-based products that much more machine-workable. Manganese deserves a mention here, too, for this metal makes already corrosion-resistant aluminium alloys almost rustproof.
Assessing the Machinability Factors
Unfortunately, by improving one material property, a second desirable property can end up hamstrung. Take alloy variants 1100 and 3003, grades that are machinable. These aren’t arbitrary labels, they’re assigned by the fabrication industry. Working with alloy graded 1100 aluminium, this relatively soft metal is workable and weldable. As for series 3003, this variant possesses moderate strength. Again, it’s a machine-expediting choice. Furthermore, this general-purpose alloy is weldable. Now, having made a case for aluminium machinability, we flip the processing model upside down. This time, the shop is working on 6063 sheeting. This architectural alloy isn’t an easy material to machine. Likewise, 7075 aluminium is one of the most robust forms of aluminium, but it’s also rigid, and therefore difficult to machine.
A Three-Factor Machinability Index
The alloy grade is selected, and the metal is ductile, workable, and weldable. Is the equipment configured to machine the metal sheets correctly? Saw blades and drill heads fitted, bending pressures and curve radii configured, and all, the second machinability factor is set. Third, and just as important as the first two machining factors, the chemical composition of the aluminium needs to advance the tooling work, not hinder the operation. An attractive, polished finish is all very well, but is there a reason that finish might hamper a weld or stop extrusion action in its tracks?
Ideally, machine shops follow the production process from the milling and grade-selection stage to the machining phase and any application-mandated post-production activities. The first job here is to select an aluminium alloy that satisfies the desired application, of course. Rust-resistant, strong, and attractively finished, who can blame a fabrication shop for focusing on the results? Unfortunately, by skipping the machinability issue, a fabrication shop creates more problems than solutions. That selected grade of aluminium alloy must be workable and weldable.
Stecor Engineering & Fabrication
1/13 Crawford St, Braeside VIC 3195
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Phone: (03) 9028 4130
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